Better by Design: Microstepping drives

Oct 01, 2011

Stepmotors or steppers are used in myriad industries today, because they're affordable and reliable. The advent of microstepping drives in particular has improved stepmotor smoothness and accuracy, spurring their use in everything from electronic printers and disk drives to aircraft controls and CNC applications.

Even so, though microstepping is quite common, microstepped motors are subject to vibration, noise, and harmonic resonance because of the way they are driven. These problems can wreak havoc: In CNC applications, for example, they can break tooling operating at higher speeds, and induce chatter that creates flaws when cutting arcs or circular shapes.

SoftStep drives, developed by Testra Corp., Tempe, Ariz., aims to overcome problematic noise and vibration. They essentially convert data into ultra-fine microstepping — 256 microsteps per motor step — and ramp speeds up and down between steps to create smooth motion without the traditional stepper clicking, buzzing, or whining noises, even at high speeds. More specifically, onboard processors treat input steps as small vector moves and smoothly chain them together.

No more chips

Align-Rite Tool Co., Tucson, makes CNC routers, mills, and other tools used by fabricators in woodworking, jewelry, metalworking, and solid-surface industries. “Those using our smaller bits — to make pool cue inlays, for example — require a CNC router that can run fairly fast, but smoothly,” says Matthew Dunne, president of Align-Rite. Here, SoftStep speeds cutting because the drives virtually eliminate vibration, smoothing movement on X, Y, and Z axes. “In fact, the steppers were so quiet that I thought the machine wasn't running,” says Dunne.

In another application, CAMaster CNC, Cartersville, Ga., uses SoftStep drives on its three-axis Stinger CNC router. Designed for light industrial use, the Stinger is a three-axis benchtop version of an industrial-duty servo-controlled router. Explains Joey Jarrard, CAMaster co-owner, “Most steppers produce a growl that sounds unprofessional — so after trying a few other driver packages, we chose a SoftStep.” The four-axis system has power, drivers, connectors, and PC cables, plus allows addition of a lathe without extra wiring. Lack of vibration allows production even down to a couple of thousandths of an inch without necessitating the smoothing out of nicks. “The drive also holds when it's not moving, but doesn't crank out the maximum amperage that can make the motor hot,” Jarrard says. “That protects users from burning by a 130° or 140° motor.” Running cooler also extends motor life.